A profile-steel beam is normally supported on rollers as it is passed through various cutting, boring, and shearing machines. To insure perfect positioning of the workpiece with respect to these machines it is normally gripped tightly at one end by a manipulator which pushes and holds the workpiece in the appropriate positions with a high degree of accuracy.
To achieve this the manipulator must very securely grab the workpiece. The manipulator normally is carried on a carriage displaceable in the desired direction. The manipulator itself has upper and lower jaws. The lower jaw is fixed and has an upper surface lying normally just below the level at which the workpiece is supported on the roller table. The upper jaw can be pivoted between an open position relatively far from the lower jaw and a closed position relatively close to it. Normally the jaws are formed so that they are complementary to the profile of the workpiece being gripped, whether it be I-section, L-section, T-section, flat, V-shaped, or U-shaped.
The disadvantage with this arrangement is that occasionally the end to be gripped is bent slightly downwardly or mushroomed slightly from previously operations. In such a system as the carriage carrying the manipulator is advanced to grip the end of the workpiece the lower jaw cannot slide under the workpiece. The machine operator must therefore lift the workpiece slightly to place it on the lower jaw before the workpiece can be gripped by the manipulator. Such an operation obviously slows down the production.